Computational modeling of nasal nitric oxide flux from the paranasal sinuses: Validation against human experiment

Clinical Applications of Nasal Nitric Oxide in Allergic Rhinitis: A Review of the Literature

Allergic rhinitis, a common allergic disease affecting a significant number of individuals worldwide, is observed in 25% of children and 40% of adults, with its highest occurrence between the ages of 20 and 40. Its pathogenesis, like other allergic diseases, involves innate and adaptive immune responses, characterized by immunologic hypersensitivity to environmental substances. This response is mediated by type 2 immunity. Within type 2 allergic diseases, certain molecules have been identified as clinical biomarkers that contribute to diagnosis, prognosis, and therapy monitoring. Among these biomarkers, nitric oxide has shown to play a key role in various physiological and pathological processes, including neurotransmission, immunity, inflammation, regulation of mucus and cilia, inhibition of microorganisms, and tumor cell growth. Therefore, measurement of nasal nitric oxide has been proposed as an objective method for monitoring airway obstruction and inflammation in different settings (community, hospital, rehabilitation) and in various clinical conditions, including upper airways diseases of the nose and paranasal sinuses. The purpose of this review is to analyze the potential mechanisms contributing to the production of nasal nitric oxide in allergic rhinitis and other related health issues. Additionally, this review aims to identify potential implications for future research, treatment strategies, and long-term management of symptoms.

Nasal nitric oxide flux from the paranasal sinuses

PURPOSE OF REVIEW

Upper airway nitric oxide (NO) is physiologically important in airway regulation and defense, and can be modulated by various airway inflammatory conditions, including allergic rhinitis and chronic rhinosinusitis - with and without polyposis. Paranasal sinuses serve as a NO 'reservoir', with concentrations typically exceeding those measured in lower airway (fractional exhaled NO or FeNO) by a few orders of magnitude. However, the dynamics of NO flux between the paranasal sinuses and main nasal airway, which are critical to respiratory NO emission, are poorly understood.

RECENT FINDINGS

Historically, NO emissions were thought to be contributed mostly by the maxillary sinuses (the largest sinuses) and active air movement (convection). However, recent anatomically-accurate computational modeling studies based on patients' CT scans showed that the ethmoid sinuses and diffusive transport dominate the process.

SUMMARY

These new findings may have a substantial impact on our view of nasal NO emission mechanisms and sinus physiopathology in general.

Numerical study on the distribution of nitric oxide concentration in the nasal cavity of healthy people during breathing

BACKGROUND

In the nasal cavity, nitric oxide (NO) is involved in many physiological functions, including antibacterial and antiviral activity, promotion of nasal mucociliary clearance, and regulation of blood vessel expansion in the nasal mucosa. We investigated the distribution of NO concentration in the nasal cavity of healthy individuals during breathing.

METHODS

A three-dimensional numerical model of the nasal airway, including the bilateral maxillary sinuses, was created to simulate NO distribution in the nasal cavity during normal breathing. The effect of different nasal airflow velocities and NO concentrations in the maxillary sinus on NO distribution in the nasal cavity was evaluated. The NO concentration in the nasal exhalation of 50 healthy people in Dalian was measured using an NO analyzer, and the growth rate of the NO concentration in the nasal cavity was measured under breath-holding conditions.

RESULTS

The distribution of NO concentration in the nasal cavity of healthy people during breathing was obtained from numerical simulation results. Lower the airflow rate, higher was the NO concentration and greater was the diffusion range in the nasal cavity. The NO concentration in the nasal cavity increased with an increase in its concentration in the maxillary sinus, indicating a linear relationship. The NO concentration in the nasal exhalation of healthy people in Dalian and the growth rate of the NO concentration in the nasal cavity under breath-holding conditions were obtained through experiments. The numerical results correspond with the experimental results.

CONCLUSIONS

The NO entered the nasal cavity mainly by diffusion and followed the convection flow of the respiratory air in the nasal cavity. NO concentration in the nasal cavity was related to the respiratory airflow velocity and NO concentration in the maxillary sinus. During inspiration, NO was present only in the nasal airway posterior to the maxillary sinus ostium, whereas during exhalation, the exhaled NO diffusely distributed throughout the nasal cavity.

Targeted drug delivery to the inferior meatus cavity of the nasal airway using a nasal spray device with angled tip

BACKGROUND AND OBJECTIVE

Nowadays, by advancement in computational tools, Computational Fluid and Particle Dynamics (CFPD) technique can be used more than ever. The main aim of this study is using a nasal spray device with angled tip to deliver drug particles to the inferior meatus cavity for treatment purposes. In the present study, the drug delivery to the lower regions of the nasal cavity will be improved that has been considered less in the literature.

METHODS

For this purpose, a spray with an angled tip was used, and the deposition of sprayed particles was compared with a spray with a straight tip. Based on the objectives presented above, a realistic model of the nasal route, including facial geometry, and paranasal sinuses obtained from a series of Computed tomography (CT) scan images, as well as the geometry of a nasal spray with two types of tip were developed.

RESULTS

It is observed that by using the spray with the straight tip, particles were mainly deposited in the middle and superior regions of the nasal cavity and no particles entered the inferior meatus airway. The results proved that the spray with the angled tip improved the regional deposition percentage in the inferior meatus cavity up to 2.4% of the total sprayed particles and 1 mg drug mass delivered to this region. The majority of these particles had a diameter between 15-55 µm and that could be considered by spray designers to produce more compatible sprays with the targeted region. Also, most particles were deposited near the inferior meatus cavity and so there is a strong chance to be absorbed and delivered to this region.

CONCLUSION

The deposition pattern and particle size contour due to the spray with the angled tip can give sight to the designers and producers of nasal sprays to build more efficient types for better targeted drug delivery purposes. With this spray type, deposited particles were observed in the inferior meatus that never happened with the straight type. Also, the angled tip of the nasal spray shows the benefit of the ease of use for the user.

Use of computational fluid dynamics (CFD) to model observed nasal nitric oxide levels in human subjects

BACKGROUND

Upper airway nitric oxide (NO) is physiologically important in airway regulation and defense, and nasal NO (nNO) levels typically exceed those in exhaled breath (fractional exhaled NO [FeNO]). Elevated concentrations of NO sampled from the nose, in turn, reflect even higher concentrations in the paranasal sinuses, suggesting a "reservoir" role for the latter. However, the dynamics of NO flux within the sinonasal compartment are poorly understood.

METHODS

Data from 10 human subjects who had previously undergone both real-time nNO sampling and computed tomography (CT) scanning of the sinuses were analyzed using computational fluid dynamics (CFD) methods. Modeled and observed nNO values during the initial 2-s transient ("spike") during nasal exhalation were then compared.

RESULTS

Examining the initial 2-s transient spike for each subject (as well as the pooled group), there was a statistically significant correlation between modeled and observed nNO levels, with r values ranging from 0.43 to 0.89 (p values ranging from <0.05 to <0.0001). Model performance varied between subjects, with weaker correlations evident in those with high background (FeNO) levels. In addition, the CFD simulation suggests that ethmoid sinuses (>60%) and diffusion process (>54%) contributed most to total nasal NO emissions.

CONCLUSION

Analysis of this dataset confirms that CFD is a valuable modeling tool for nNO dynamics, and highlights the importance of the ethmoid sinuses, as well as the role of diffusion as an initiating step in sinonasal NO flux. Future model iterations may apply more generally if baseline FeNO is taken into account.